1. Field of the Invention
The present invention relates to a core embedded rubber crawler, particularly a rubber crawler in which a plurality of longitudinally spaced cores are embedded in a width direction of the rubber crawler, sprocket engagement holes are perforated between the cores, and two rows of longitudinally spaced tread members are disposed on the left and right side of the outer peripheral grounding surface of the rubber crawler.
2. Description of the Related Art
In FIG. 4, a core embedded rubber crawler, which is a typical example of a conventional rubber crawler is widely used. As shown in FIG. 4(A), the rubber crawler 21 has a main body 22 in the form of an endless belt. To enhance a transverse rigidity of the main body 22 of the rubber crawler 21 and a driving force resistance on driving the rubber crawler 21, a plurality of longitudinally spaced cores 23 are embedded in a width direction of the rubber crawler 21. As shown in FIG. 4(C) of the C-C cross-section in FIG. 4(A), in order to enhance the longitudinal rigidity of the main body 22 of the rubber crawler 21 and the driving force resistance, if necessary, a reinforcing cord 26 embedded in the main body 22 of the rubber crawler 21 approximately at the intermediate part thereof with respect to the thickness direction is arranged on an outer peripheral grounding side of the core 23. The reinforcing cord 26 is obtained by placing a number of reinforcing filaments 26A, 26B side by side and applying a treatment such as rubberizing thereto. Such rubber crawler is referred to as a core and cord embedded rubber crawler.
In this conventional example, as shown in the bottom view of FIG. 4(B), sprocket engagement holes 25 are perforated between the longitudinally spaced cores 23 embedded along the centerline of the rubber crawler 21. The rubber crawler 21 has two rows of longitudinally spaced tread members 28A, 28B which are alternatively disposed on the left and right sides of the outer peripheral grounding surface of the rubber crawler. Also, for protecting the core 23 and ensuring a tractional force, the rubber crawler 21 has a central lug 29 which constitutes a part of the main body and is arranged in the connection section between the tread members 28A and 28B to connect the tread members to each other in a position embedding the core 23. In this type of the core embedded rubber crawler as shown in FIG. 4(C), both of left and right sides of the core 23 of the outer peripheral grounding side on which the reinforcing cord 26 is embedded are thinly constructed, and the central section of the core 23 engaged by a sprocket is thickly constructed for reinforcing. As a result, it is necessary to reduce relatively the thickness of the section of the central lug 29 which connects between the tread members 28A, 28B.
Therefore, as shown in FIG. 4(A), when the rubber crawler is driven in the direction shown by the white arrow, the rubber crawler 21 moves on a road surface in the right direction of the figure while abutting the road surface and thus the rear portion of the tread member 28 or the central lug 29 (shown by the black arrow) allows a tractional force to act on the road surface. Based on FIG. 5 of a macrograph of this section (corresponding to “B” of FIG. 4(B)), the force acting on to each components of the rubber crawler is analyzed by a relation between the tractional force of the rubber crawler (sprocket driving force) and the resistance force of the surface. As mentioned above, to ensure a volume of a rubber, the central lug 29 is structured to have a face perpendicular to the running direction of the rubber crawler, so that the core 23 can be protected and the tractional force can be sufficiently obtained. Also, in order to ensure a directional stability of the rubber crawler, a driving surface of the rubber crawler, which is the rear side with respect to the running direction on forth movement, is configured to have a two step inclination, and to make the rear inclined surface of the central lug 29 and the tread member 28B to have the approximately same height as each other.
In the central lug 29, {circle around (1)} a shearing stress by the driving force acts on an interface between the core 23 and the central lug 29, {circle around (2)} compressive forces generated perpendicularly from the road surface act on the outer peripheral grounding side of the central lug 29, and {circle around (3)} a rotational force from the road surface showing tendency stripping the lug is given to the rear inclined surface of the central lug 29. These forces largely affect the vicinity of the central lug 29 which faces to the sprocket engagement section to which the sprocket driving force directly acts on. Thus, a peeling of the rubber easily occurs in the vicinity of the central lug 29. A cutting damage by the forces {circle around (2)} and {circle around (3)} owing to in the vicinity of the central lug 29 the resistance force of the surface and the impediment is given, resulting in reducing the rigidity of the central lug 29. In addition to these, the force {circle around (1)} is applied to the tread members 28A, 28B connecting to the central lug 29, which are peeled off. As a result, as shown in FIG. 6, the peeling which occurred in the vicinity of the central lug 29 leads to the peeling on the tread members 28A and 28B.
FIG. 7 includes graphical representations for driving times of the rubber crawler having a conventional central lug which drove on a rough road such as gravel for a long time, In the figure, the driving times of the rubber crawler are 20 h, 70 h and 100 h from top (A) to bottom (C). After 20 h, it is observed that the central lug 29 including both sides of the tread members slightly abrades. After 70 h, it is found that an exposure of the core 23 caused by the peeling of the central lug 29 partially occurs. After 100 h, the central lug 29 mostly peels and the core 23 emerges, and furthermore the reinforcing cord 26, for example made of steel, partially emerges, Therefore, in addition to a corrosion-cut of the reinforcing cord 26, a protection ability of the core 23 by the central lug 29 completely disappears and a life of the rubber crawler remarkably reduces.